If you encountered this error, you should visit Microsoft's web-site and individualize your Windows Media Player:
Open Internet Explorer and visit the following page:
services.wmdrm.windowsmedia.com/indivSite.

Click "Upgrade" and follow the process to complete the individualization process.

If the "Upgrade" button is not present, simply open any DRM protected content in Windows Media Player, and it will promt you to install the IBX components that you.